Thin section tomography of the sella turcica and endocrine assays have allowed the early diagnosis of many pituitary tumors. Controversy exists regarding the following questions: Does abnormal thin section tomography always reflect intrasellar pathology or are a variety of changes misinterpreted such as pituitary asymmetry or hyperplasia, the empty or partially empty sella and congenital sphenoid bone variations? Has the percentage of incidental pituitary adenomas changed from that reported by earlier pathology investigators such as Costello (1936) who noted 22.5% in his series? What is the predominant cell type of these adenomas and are they associated with tomographic and histologically verified sella bone erosion? The present study seeks to help answer these questions by performing hypocycloidal polytomography on 200 en bloc necropsy sphenoid bone specimens. The interpretation of these films will be compared with the stained microscopic histology of these same decalcified specimens with the pituitary in situ. The clinical history of each autopsy will be thoroughly reviewed.